Mr. Kitty would later have prominent role in "Cat Orgy", in which his/her gender has shifted back towards female and he/she is in heat. After attempting to have sex throughout the episode, Mr. Kitty assembles a massive group of male cats to come home with her. She then proceeds to get all the cat's high on catnip (which they snort like cocaine) and all the male cats proceed to take turns having sex with Mr. Kitty. Cartman and his babysitter Shelly Marsh were, needless to say, horrified.

Although Mr. Kitty is indicated to be female in "Cat Orgy", there are examples of where he's portrayed as a male; in the season 12 episode "Major Boobage", the children experiment with Mr. Kitty's urine after learning that the urine of male cats can cause intoxication, indicating that Mr. Kitty is actually male.

Mr Cartman always refers him as Mr. Kitty. Mr. is always used for male.

Mr. Kitty would later have prominent role in "Cat Orgy", in which his/her gender has shifted back towards female

Mr. Kitty's next real appearance would be in "Major Boobage", in which Cartman, Kenny, Kyle and Stan attempt to test whether or not
it's possible to get high off of male cat urine (Mr. Kitty is again
male in this episode).

It appears that changes are made from episode to episode, from Mr Kitty's nose color to Mr Kitty's gender. This is most probably due to a writer's mistake or just ignorance. We can still assume that Mr kitty might be bisexual or transgender, but I don't have confirmations from any canon sources.